Fix incorrect stream example (#1689)
Fix incorrect stream example (#1689)

The example was calling #stream on the wrong object.

[closes #1688]
dazuma/google-cloud-ruby,googleapis/google-cloud-ruby,dazuma/google-cloud-ruby,landrito/google-cloud-ruby,landrito/google-cloud-ruby,googleapis/google-cloud-ruby,googleapis/google-cloud-ruby,qingling128/google-cloud-ruby,blowmage/gcloud-ruby,dazuma/google-cloud-ruby,CloudVLab/google-cloud-ruby,quartzmo/google-cloud-ruby,CloudVLab/google-cloud-ruby,quartzmo/google-cloud-ruby,googleapis/google-cloud-ruby,googleapis/google-cloud-ruby,landrito/google-cloud-ruby,quartzmo/google-cloud-ruby,CloudVLab/google-cloud-ruby,dazuma/google-cloud-ruby,dazuma/google-cloud-ruby,CloudVLab/google-cloud-ruby,quartzmo/gcloud-ruby,quartzmo/google-cloud-ruby,qingling128/google-cloud-ruby,CloudVLab/google-cloud-ruby,landrito/google-cloud-ruby,quartzmo/google-cloud-ruby,quartzmo/google-cloud-ruby,googleapis/google-cloud-ruby,qingling128/google-cloud-ruby,landrito/google-cloud-ruby,dazuma/google-cloud-ruby,qingling128/google-cloud-ruby